So the weather cooperated in giving this row cover thing a real test: I put it up on November 9 and then it was COLD for about 10 days. I uncovered for the first time the day after Thanksgiving and you can see the results at the right (row cover pulled back) and below (harvested November 28).

Conclusion: The row cover really does work. (All you more experienced gardeners can now say DUH! and gloat.)